Conversion of the soluble protein, fibrinogen, to the insoluble polymeric form, fibrin, is critically important to normal hemostasis. The exact size, shape, and mode of polymerization of fibrinogen molecules are not certain; determination of these structural parameters is the central theme of the proposed research. The physical properties that define the biological role of fibrin--insoluble clot formation--make it a difficult subject for structural analysis. We have shown that brief treatment of fibrinogen with a plasmin-like enzyme from Pseudomonas alters the interaction properties of fibrinogen. When this modified fibrinogen is reacted with thrombin, fibrin-like fibers form; alternatively, when the modified molecule is precipitated out of solution under low ionic strength conditions, micro-crystals and crystals form, suitable for study by electron microscopy and X-ray diffraction. I propose to determine the nature of the chemical changes that the enzymes from Pseudomonas causes in the fibrinogen molecule by end group analysis, chromatographic, electrophoretic techniques and ORD/CD measurements and to correlate these data with electron microscope and X-ray diffraction results. These experiments may give some insight into the three dimensional structure of the fibrinogen molecule and indicate some of the spatial relationships among fibrinogen molecules in the fibrin clot. The clotting process, in vivo, is a delicate balance of many sequential and simultaneous events. Knowledge of both the physical and chemical structure of the fibrinogen molecule is critical to the understanding and control of metabolic disorders relating to the structure and function of the fibrinogen molecule.